Moisture and air sensitive or reactive materials are often shipped in drums or pails to a point of use and are removed from their containers by a simple pump if the material is not too viscous, or with a special type of pump which includes a heating platen if the material is highly viscous or a meltable solid. In the latter case a heated platen is placed against the exposed upper layer of the material stored therein to render it plastic, and the softened material can then be made to flow through an outlet passage to be used in its intended manner. Certain of such materials have a high sensitivity to exposure, to moisture or air, and some are even rendered useless by such exposure to moisture in the atmosphere. Moisture curable polymeric hot melt adhesives containing reactive isocyanate or siloxane end groups and sold commercially as Bostick Supergrip 2000, Fuller Ipatherm, Ceca Recticol and Reichold Swift are typical examples. These polymeric materials are viscous liquids at room temperature and remain in that condition until exposed to moisture, at which point the isocyanate or siloxane groups react, causing the liquid adhesive to cross link and become essentially thermoset.
When these types of polymeric materials are packaged for storage and shipment in commerce, exposure to moisture must be precluded, otherwise the foregoing undesirable reaction can occur at the exposed surface of the stored material which prevents the emptying of the container by pumping it out of the drum with the heated platen. More or less successful sealing means have been used hereintofore wherein the exposed layer of the stored moisture sensitive material has been blanketed with a layer of carbon dioxide, or it has even been suggested that bags containing desiccants be sealed in the drum over the top of the exposed layer of stored material. For one reason or another neither one of the presently available sealing means has been found to be completely satisfactory under all of the variable conditions that are found to be present when air or moisture reactive materials must be stored in a container for ultimately cooperating with a pumping means and then shipped to a point of use.